One popular 'isekai ojisan light novel' could be 'Isekai Ojisan: Isekai ni Tensei Shita Kedo Cheat Nanka Shinai yo'. It tells an interesting story about an uncle who gets isekai -ed but doesn't have the typical cheat skills.
For me, 'That Time I Got Reincarnated as a Slime' stands out. The world-building and plot development are really engaging. Also, the characters have a lot of depth.
Well, it's a bit hard to pinpoint exactly which was the very first one. But some early examples could include 'El-Hazard: The Magnificent World', which had elements of the isekai genre.
Isekai Quartet indeed has a manga. It offers a different perspective and sometimes delves deeper into the story compared to the anime. The manga can be a great companion to the animated version for fans wanting more of the Isekai Quartet world.
I'm not entirely sure as I haven't read it in detail. But generally, it might be about some sort of fantasy story involving a bishoujo (a cute girl character in Japanese media) and an ojisan (uncle or older man) in a novel - like setting.
I'd recommend checking out online manga libraries such as Comixology or Crunchyroll Manga. They often have a good selection of isekai titles. Also, some local libraries might have physical or digital copies you can access.
Isekai manga is a genre where the main character gets transported to another world. It's different from others because of the focus on this world-jumping aspect and the adventures that follow.
I'm not sure who the main characters are exactly as I don't know this work well. But from the title, it seems that a bishoujo and an ojisan would be important characters.
For must-read isekai manga, 'Sword Art Online' is a great choice. It combines action, adventure, and a touch of romance. The virtual world it creates is both exciting and immersive.